Buy some CFL's for the Veg room # 18 hrs under CFL is going to be a lot cheaper and you shouldn't need the wattage in veg

You could then double up with the 2x 600wHPS in flower and go for big yields. Maybe using both lights in the last few weeks of flowering so you get the most yield and lowest energy costs.

Messing with the timing will just cause your plants stress, drop yield and likely cause hermy attributes if the plant is stressed and then flowered. I would seriously consider a smaller veg room light.

Just an idea to chop costs! Hell even Envirolights can veg weed nicely. Or invest in a 250w HPS for Veg.
Delta9 UK Reviewed by Delta9 UK on . ELECTRICITY SAVING I saw my electric bill today, not good. I currently have 2- 600w HPS, one on an 18 cycle, the other on 12. Could I run the 18 hour for only 12 hours, with say, an hour ON in the middle of the dark cycle to prevent flowering ? It WOULD save electric, but would i get enuff growth ? Comments appreciated. V. Rating: 5